1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a technology effectively applied to a liquid crystal display device that uses a column spacer to give pixels a uniform cell gap.
2. Description of the Related Art
More and more uses are being found for liquid crystal display devices (liquid crystal displays) because of their features such as high display quality and the ease of reduction in thickness, weight, and power consumption. The various uses of liquid crystal display devices include a display (monitor) for cellular phones, digital still cameras, and other portable electronic devices, a display for personal computers, a display for printing and designing, a display for medical equipment, and a liquid crystal television set.
With the expansion of uses mentioned above, the demand for liquid crystal display devices to have a higher image quality is ever increasing in recent years. In medical equipment displays and liquid crystal television sets, in particular, the quality of image display in black color is very important, and a liquid crystal display device capable of displaying uniformly in black without unevenness at a low luminance is seriously sought after.
A display panel used in a liquid crystal display device (liquid crystal display panel) is structured such that a liquid crystal material (liquid crystal layer) is placed between a pair of substrates, and has a display area constituted of many pixels. The liquid crystal display panel employs, for example, a method of dispersing bead spacers (spherical spacer members) between the paired substrates or a method of forming column spacers on any one of the paired substrates to make the liquid crystal layer thickness (cell gap) uniform in each pixel. The method of forming column spacers on any one of the paired substrates is mainly employed in liquid crystal display panels for liquid crystal display devices that are required to have high image quality.
A variation of the method of forming column spacers on any one of the paired substrates has been proposed in which misalignment between the top of a column spacer and a column spacer receiving portion, which is provided on the other substrate where no column spacers are formed, is prevented by providing the column spacer receiving portion with a protrusion and fitting the protrusion into the column spacer (see, for example, JP 2006-330470 A).
Providing a mount (protrusion) in the column spacer receiving portion on a substrate where no column spacers are formed as in a liquid crystal display panel described in JP 2006-330470 A may solve the problem of light leakage due to misalignment between the substrates which is caused when, for example, surface pressing is performed on the liquid crystal display panel.
However, an examination by the inventors of the present invention has revealed that providing the mount (protrusion) does not prevent minute bright spots from appearing all over the panel when the liquid crystal display panel is given a slight shake. This indicates that vibrations applied during the transportation of the liquid crystal display panel or other times cause minute bright spots within the screen, thus posing a serious problem for image quality improvement, in particular, display quality improvement in a low luminance (low gray scale) part such as a part displayed in black color.
A research conducted by the inventors of the present invention has revealed that the minute bright spots mentioned above are caused by a mechanism in which an alignment film between the column spacer and the mount is chipped due to vibrations applied to the liquid crystal display panel, and flakes of the alignment film floating in the liquid crystal within the display area disturb the alignment of the liquid crystal.